The precision of a caliber depends upon the quality of its regulating member, and very high oscillation frequencies, for example of 10 Hz, compared to the usual frequencies of 2.5 to 4 Hz, are only obtainable if suitable regulating members are conceived, in particular as regards the balance.
Indeed, the energy to be provided for maintaining oscillation, in the form of elastic balance spring torque, is proportional to the product, on the one hand, of the inertia of the balance about the pivoting axis, and, on the other hand, of the square of the frequency. Thus, for example, for the same energy, a frequency change from 4 Hz to 10 Hz results in the inertia being divided by approximately 6. For a frequency of 4 Hz, balance inertia of 12 mg·cm2 is considered to be good, since this type of balance conventionally has a diameter of 9 to 10 mm. Thus, a balance for use at 10 Hz must have a low inertia value, in particular less than 2 mg·cm2.
For optimum operation, a balance for use at 10 Hz must also have minimal mass, notably less than 30 mg, so as to reduce friction in the bearings, to avoid isochronism disturbance in the various positions of use.
Although it has low mass and inertia, the balance of a high frequency oscillator must also allow adjustment of the unbalance and perfect poising, both static and dynamic, and the construction thereof must make setting and/or adjustment operations possible. It is not therefore possible to use conventional technology, or solutions with lighter balances such as the balances wherein the felloe has spokes disclosed in FR Patent No. 1275 357 in the name of Straumann, or FR Patent No. 1 301 938 in the name of LIP. Indeed, even the reduced mass of these balances does not provide sufficiently low inertia. Likewise, the mass and inertia of a titanium balance in accordance with EP Patent No. 1 562 087, in the name of MONTRES BREGUET SA and devised with a titanium felloe and arms and reduced sections, are still greater than required for optimum operation.
FR Patent No. 998 791 A in the name of JAEGER ETS discloses a balance with adjustable inertia, including flexible felloe arms which can be screwed into a particular position. EP Patent No. 2 104 008 A1 in the name of NIVAROX SA discloses a single-piece silicon sprung balance unit. CH Patent No. 471 410 A in the name of LANGENDORF WATCH CO also discloses a balance with a flexible felloe that can be adjusted using screws.
A Q factor on the order of 500 is also sought, thus considerably higher than that of conventional oscillators where, for good quality watches, the Q factor is close to 220 to 280. This Q factor can only be obtained by combining a silicon or similar balance spring with a balance that satisfies the above conditions. In addition to obtaining a high Q factor, combined with setting and adjustment possibilities, the index-assembly must also be omitted.
Moreover, since the mass of the unit is limited, the smallest possible number of components should be preferred.
However, micro-machinable materials, such as silicon and quartz, which are theoretically made in finite dimensions, with very precise tolerances, are not easy to machine subsequently.
It is therefore necessary, for regulating members made of such materials or incorporating at least one component made of this type of material, to have the possibility of frequency and/or inertia adjustments, but by avoiding machining and by prioritising setting possibilities.